The Collaborative International Dictionary of English v.0.48:
Fifth \Fifth\, a. [OE. fifte, fifthe, AS. f[imac]fta. See
1. Next in order after the fourth; -- the ordinal of five.
2. Consisting of one of five equal divisions of a thing.
Fifth monarchy men (Hist.), a fanatical sect in England, of
the time of the commonwealth, who maintained that there
would be a fifth universal monarchy, during which Christ
would reign on earth a thousand years.
Fifth wheel, a horizontal wheel or segment above the fore
axle of a carriage and beneath the body, forming an
extended support to prevent careening.